The present invention relates to a contact piece consisting of an insulating mass for establishing delta circuits on three-legged transformers, especially for the predetermined interconnection of the high end voltage windings of three-phase current, air-cooled transformers of the type having six connecting elements on the exterior surface thereof.
The winding connecting contacts of high end voltage windings of transformers are normally located at the ends of the windings. Consequently, the distance between the connecting contacts of each phase or of the contacts between the phase for transformers of different types and sizes are typically unequal. This is true especially for air-cooled transformers which are made in accordance with the so-called wet winding process.
Heretofore, the connections of such winding connecting contacts have conventionally been produced by providing properly dimensioned conducting wires, whereby attention was paid to the fact that a sufficient air gap must be maintained in the crossing point so that sparkover or creeping current would be prevented with a high degree certainty. Furthermore, it has been known to use switching strips in cast resin transformers which are always provided with six connecting elements (connecting contacts) on the exterior thereof (see, German Utility Pat. No. 1,971,623 . Generally however, conventional switching strips may not be used for air-cooled transformers produced by the wet winding process since the connecting contacts are always located at the foot and at the head of windings. The known connecting strips are also not advantageous for the connections of high end voltage windings since for transformers of various types and sizes, various switching strips must always be maintained in inventory storage.
Therefore, the task arises of providing a contact piece for establishing delta circuits, especially for the connection of the high end voltage windings of air-cooled transformers, which may be mounted in a simple manner and is suitable for various types, sizes and kinds of windings.
This task is solved by the contact piece of the present invention wherein six connecting elements are disposed in the general shape of a star and are connected to one another by a centrally located base body having conducting lines embedded therein. The connecting contacts at the distal ends of the connecting elements themselves maintain the required minimum distance for the prevention of creeping currents and spark-over.
The term "connecting elements" as used herein and in the accompanying claims also includes the possibilities that the connecting contacts either outwardly project for a short distance from the base body or are peripherally countersunk into the base body.
Preferably, the conducting cables embedded inside the base body are connected in such a manner that the connecting elements as numbered clockwise in accompanying figures with Roman Numerals I, II, III, IV, V and VI are always interconnected in pairs and, more particularly, 16.sub.I is connected with with 16.sub.V ; 16.sub.II is connected 16.sub.IV ; and 16.sub.III is connected with 16.sub.VI. With this configuration of the conducting cables, it is possible, as will be explained in more detail below, to establish various circuits customary in the field of transformer construction merely by selecting the specific orientation of the connecting element of the present invention relative to the contacts of the transformer. Thus, the same connecting element may be utilized to achieve various circuit configurations. The outside lying connecting contacts at the distal ends of the connecting element are electrically interconnected in pairs with the winding connecting contacts by conventional insulated and correspondingly extended connecting cables.
Preferably, the connecting elements are disposed in a radially symmetrical manner and thus all connecting elements may be electrically charged simultaneously. Preferably, the base body has a cylindrical or hexagonally-prismatic shape in which the conductive cables are embedded. The peripheral connecting members are molded with the base in a star-shaped arrangement through which each of the conductive cables can be extended. By virtue of the connecting members and the base body, a preferred one-piece cable support is established.
Transparent areas or window areas are preferably provided in the upper side of the cable support member or in the base body so that the course of the embedded calbes can be readilly identified to facilitate installation. It is also possible to apply cable-like markings on the upper side of the cable support or base body to correspond to the course of the embedded cables. These markings may take the form of etchings of a characteristic depth on the upper side of the cable support. With the aid of the window area or markings, one may thus readily recognize at a glance the manner in which the cable lie with respect to the three transformer windings.